Download Web Services - School of Engineering and Information Technology

Web Services and Application
Development Frameworks
Supplemental Lecture
**NOT ASSESSIBLE**
ICT337 Week13 Supplemental: Web Services
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Web Services
•Web Services are used primarily as a means for
businesses to communicate with each other and with
clients.
• They allow organisations to transfer data without
knowing the details of the IT systems behind the
firewall.
•Web services do not provide the user with a GUI,
rather they share business logic, data and processes
through a programmatic interface across a network.
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Web Services
•Web services allow different applications from
different sources to communicate with each other
without
custom
coding,
and
because
all
communication is in XML, Web services are not tied to
any one operating system or programming language.
– For example, Java can talk to Perl, Windows applications
can talk with UNIX applications.
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Web Services
• Web Services is our current generation of
technologies to allow application-to-application
(program-to-program) communication by using XML.
• It covers how to:
• define modular, self-describing applications
• publish the applications so they are available
• locate these available applications from anywhere
• invoke these applications remotely
• All these using open Internet standards like XML,
HTTP and SMTP.
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Web Services
• Please note the difference between this technical
use of the word “Web Services” and the nontechnical use of “web services”, which refers to
any program available through an HTML form
over the web.
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Distributed Object Technologies
• There have been past efforts to provide programlevel object exchange:
• OMG’s CORBA/IIOP (www.corba.org/)
• Microsoft’s DCOM (www.microsoft.com/com/tech/dcom.asp)
• Java RMI (java.sun.com/rmi)
• But all of these technologies suffer from:
• Complex set-up and object invocation.
• Platform and language dependence.
• Lack of universal acceptance.
• Lack of extensibility to different problem areas.
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What is missing today?
• What is missing today is a consistent way to allow a
service (program, application) communication with
another:
• There is no consistent framework for describing how a service
can be invoked. eg. how do I use a particular PHP application?
• There is no consistent framework for listing available services,
and how clients can discover them. eg. how do I find out what
other PHP applications are available?
• Location of services on the web and how to use them have to be
manually determined, and then manually invoked - they can’t be
done by programs automatically.
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Developing Web Services
• Various companies and organisations have taken
strong initiatives to gain and maintain the loyalty of
software developers as we move towards Web
Services.
• The two biggest initiatives:
• SUN and the Java approach
• Microsoft’s .NET
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Microsoft .NET
• .NET is a model targeted at migrating Microsoft’s
focus from desktop-based software towards
Internet-based software.
• Uses XML as the basis for data exchange.
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Components of .NET
• Different parts of the .NET initiative:
• Tools for software developers
» Visual Studio .NET
» the .NET Framework (consisting of a runtime engine CLR,
languages ASP.NET and C#, XML classes, etc)
• .NET Enterprise Servers
» where all the data will reside and be served from
» e.g.. BizTalk 2000, Commerce Server 2000, SQL Server 2000, etc.
• .NET operating systems.
• Building Block Services.
» Collections of complete services for integrating into other software.
» e.g.. Passport .NET for user authentication
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Sun’s ONE
• Sun Microsystems's future vision of web services is
based on its Open Net Environment (ONE) initiative.
• Heavy promotion of developments in Java
technologies
• Especially in its J2EE (Java 2 Enterprise Edition)
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Platform Independence
• These are the two biggest initiatives in the industry
today to lock Internet service and application
developers into one environment.
• Microsoft claims programming language
independence with .NET (ONE uses Java), while
Sun claims operating system independence with
ONE (.NET requires Microsoft OS and servers to
operate).
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Advantages claimed by .NET
• Cross-language development.
• Power and Integration of Visual Studio.Net as a
development tool.
• Simpler programming model - easier to pick up.
• Interweaved with the operating system - makes
use of the powerful facilities available.
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Advantages claimed by Java
• Proven technology in the enterprise environment.
• Systems portable to other operating systems.
• More advanced and powerful programming
model.
• Standards developed by an industry instead of
one vendor.
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Other Frameworks
• Other organisations also push their own versions of
development frameworks, although not as extensive
or as fanatically, as Java or .NET.
• eg.
• IBM’s WebSphere
» http://www-3.ibm.com/software/info1/websphere/index.jsp?tab=highlights
• BEA’s WebLogic
» http://www.bea.com/products/weblogic/platform/index.shtml
• Apache XML Project
» http://xml.apache.org/
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Web Service Example
Source: http://msdn.microsoft.com/library/default.asp?url=/library/enus/cpguide/html/cpconwebservicesinfrastructure.asp
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Components of Web Services
• In Web Services, we
• describe a service using the Web Services Description Language
(WSDL).
• define a way to publish and discover information about Web services
using Universal Description, Discovery and Integration (UDDI),
and
• invoke the service using Simple Object Access Protocol (SOAP).
• We will look at WSDL and SOAP.
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WSDL
• A WSDL document describes
– What the service can do
– Where it resides
– How to invoke it
• WSDL are like IDL but lot more
flexible and extensible
• Defines binding for SOAP1.1,
HTTP GET/POST and MIME
• WSDL descriptions can be
made available from an UDDI
registry
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WSDL1.1 Document
Structure
WSDL
Document
[Types]
{Messages}
{Port Types}
{Bindings}
{Services}
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WSDL
• WSDL can be generated dynamically by web
service frameworks, or from scratch.
• Creating a WSDL from scratch allows for a great
deal of flexibility and makes it easier for
consumers of web services to create clients when
not using proxy-generated classes.
• WSDL has the ability to specify a specific ordering
of element, cardinality and optionality, etc.
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SOAP
• XML based protocol for
exchange of information
– Encoding rules for datatype
instances
– Convention for representing
RPC invocations
• Designed for looselycoupled distributed
computing
– No remote references
• Used with XML Schema
• Transport independent
• SOAP with Attachments
allow arbitrary data to be
packaged.
ICT337 Week13 Supplemental: Web Services
SOAP1.1 Message
Structure
SOAP
Envelope
Header
Entries
[Header
Element]
Body
Element
[Fault
Element]
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Methods of Implementing in Java
• Many text books on Web Services tend to present far too
much theory and few examples that can help you to
create your own Web Services.
• No service, regardless of its percieved benefits can be
considered useful unless there are applications, tools, and
reference materials that make development easier
• Look for very recent text books. Most of the older ones are
heavy on theory and use packages that are out of date.
Many of the examples wont work unless you can track
down an older version of the tool.
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Methods of Implementing in Java
• There are Applications/Tools that can make
creating and running your own web services in
Java very easy. The most notable include.
– Java Web Services Developer Pack
– AXIS
– Electric Glue
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AXIS
•
•
•
Axis is essentially a SOAP engine -- a framework for constructing SOAP
processors such as clients, servers, gateways, etc.
The current version of Axis is written in Java.
Supports 3 modes of services– RPC – default – Object based. AXIS hides all the complicated implementation from
you.
– Document/Wrapped – uses plain XML.
– Message based – XML contained in java XML objects.
•
•
•
•
•
•
•
a simple stand-alone server.
a server which plugs into servlet engines such as Tomcat,
extensive support for the Web Service Description Language (WSDL),
emitter tooling that generates Java classes from WSDL.
some sample programs, and
a tool for monitoring TCP/IP packets.
A tool for monitoring raw SOAP messages.
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AXIS - Installation
• Make sure that you have
– J2SE SDK 1.3 or 1.4: We will use 1.4
– A Servlet Container: We will use Tomcat
Direcotry Structure:
– Download the AXIS package from
http://xml.apache.org/axis
• Unzip it and look at the dir. tree. Note
that Axis runs as a Servlet.
• Deploy Axis.
– Copy webapps\axis tree to webapps
directory of Tomcat.
– Alternatively, modify server.xml of Tomcat.
•
•
Run Tomcat.
Test the installation with the test JSP. Load
http://localhost/axis/happy.jsp. This script will
tell you if anything else is required.
axis
webapps
lib
docs
samples
axis
WEB-INF
lib
classes
web.xml
……
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AXIS - Setup
• The above will generally install AXIS for use by Tomcat.
• If you compile/run anything from the command line, you will need to
make the AXIS jars (axis/lib directory) visible so the java compiler and
interpreter can find them.
• You can do this by: – creating a simple batch file that adds each of these jars to the classpath.
Then run this each time you run from the command line.
– Adding each AXIS jar to the CLASSPATH environment variable in
windows. If you do it this way java can find the jars without having to do
anything supplemental.
– Create a new environment variable in windows and then include the
environment variable when you compile of run java files.
– If you are using JBuilder or similar, specify the jars as required libraries.
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Creating web services in AXIS
• Two mechanisms.
• Java Web Service (JWS) – easiest.
• Custom deployment.
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Creating web services in AXIS - JWS
• JWS
• Simple way to create basic web services
• Step 1: Create a java class with the services you want to
deploy.
• Step 2: Save the file with a .jws extension.
• Step 3: move to webapps/axis directory on Tomcat.
That’s it.
public class echo {
public String echoBack(String word)
{
return "You said "+word;
}
}
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Creating web services in AXIS - JWS
• AXIS takes care of everything for you.
• If you want to view the wsdl just append ?wsdl to
the end of the url.
• As axis creates a wsdl, the web service can be
invoked by any client on any platform using any
language (as long as it has any SOAP API).
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AXIS – JWS Clients – Manual Client
• You can create a client in one of two ways in
AXIS.
– Create a client from scratch.
– Dynamically create stubs and skeletons using
wdsl2java.
• Code can be embedded into other applications,
servlets, JSPs, etc.
• Clients that use AXIS are generally object based.
However AXIS does support pure XML exchange.
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AXIS – JWS Clients – Option 1
import org.apache.axis.client.Call;
import org.apache.axis.client.Service;
public class echoClient
{
public static void main(String [] args) throws Exception
{
String endpoint = "http://localhost/axis/echo.jws";
Service service = new Service();
Call
call
= (Call) service.createCall();
call.setTargetEndpointAddress( new java.net.URL(endpoint) );
call.setOperationName("echoBack");
String ret = (String) call.invoke( new Object [] { "Your mother" });
System.out.println("Got result : " + ret);
}
}
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AXIS – JWS Clients – Option 1
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AXIS – JWS Clients – Option 2
• In the second option we use wsdl2java to generate some skeletons
and stubs and the write a small client.
• Issue the command: java org.apache.axis.wsdl.WSDL2Java http://localhost/axis/echo.jws?wsdl
•
This will create a package with some java skeletons in it. In our case
it created–
–
–
–
localhost\axis\echo_jws\Echo.java
localhost\axis\echo_jws\EchoService.java
localhost\axis\echo_jws\EchoServiceLocator.java
localhost\axis\echo_jws\EchoSoapBindingStub.java
• EchoSoapBindingStub is the one we are concerned with. It provides
an object with a number of constructors and an echoBack method that
we can use like a normal java object.
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AXIS – JWS Clients – Option 2
import localhost.axis.echo_jws.*;
import java.net.URL;
import org.apache.axis.client.Service;
public class echoClient2
{
public static void main(String [] args) throws Exception
{
EchoSoapBindingStub ser=new EchoSoapBindingStub(new
URL("http://localhost/axis/echo.jws"),new Service());
String ret = ser.echoBack("my mother");
System.out.println("Got result : " + ret);
}
}
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AXIS – JWS Clients – Option 2
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Creating web services in AXIS – Custom
Deployment using Web Service
Deployment Descriptor (WSDD)
• JWS is easy and fast but with the following
limitations– you need to expose the source.
– the amount of configuration you can do as to how the
service gets accessed is pretty limited.
– you can't specify custom type mappings, or control
which Handlers get invoked when people are using
your service.
– Using WSDD we can run configurable services with
advanced options.
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AXIS - WSDD
• Implementing a web service using WSDD only
requires a few additional steps.
– Compile the java class, rather than just giving it a .jws
extension.
– Create a WSDD file which tells AXIS how to deploy the
class.
– Run the adminClient to send the service to the AXIS
server for deployment.
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AXIS – WSDD – deploying a service
• To deploy echo.java as a service
– Compile echo.java.
– Move echo.class to webapps\axis\WEB-INF\classes.
– Create a WSDD file
<deployment xmlns="http://xml.apache.org/axis/wsdd/" xmlns:java="http://xml.apache.org/axis/wsdd/providers/java">
<service name="echo" provider="java:RPC">
<parameter name="className" value="echo"/>
<parameter name="allowedMethods" value="*"/>
</service>
</deployment>
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AXIS – WSDD – deploying a service
• Use the adminClient to deploy the service. The –p80 at the end is
used to specify the port (needed if not running on port 8080).
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AXIS – WSDD – deploying a service
• Test the service is up and running by loading in a
browser. Note the addition of “services” in the url.
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AXIS – WSDD – deploying a service
• The clients created earlier will still work after we
modify the url.
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AXIS – WSDD – undeploying a service
• If we need to remove a web service then we need
to undeploy it.
– Create an undeploy wsdd file
<undeployment xmlns="http://xml.apache.org/axis/wsdd/">
<service name="echo"/>
</undeployment>
– Run the adminClient to undeploy the service
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AXIS – WSDD
• The process of deploying/undeploying is relatively
simple.
• Unless we need to configure the service
differently, you can copy the wsdd files and
change a couple of values which represent the
name of your class/service.
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AXIS - SoapMonitor
• Axis provides an applet that monitors raw soap
requests/responses.
• Can be used for debugging.
• Can also be used to determine the XML needed
to support a particular WSDL. WSDL files that are
generated dynamically can be a bit hard to read.
If you need the XML, you can use wsdl2java, run
the client and then you will have the necessary
XML.
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AXIS – Conclusion
• AXIS provides an easier mechanism to deploy and
consume services.
• Similar tools exist in other packages. AXIS is open source.
• AXIS can connect to other web services in other
platforms, and can process requests made from clients on
other platforms.
• A good choice when starting off in web services. You can
use the object-based implementations while you are
learning XML/XSLT, etc.
• If you are not undertaking serious development in web
services, you wont have to learn XML at all.
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References
• ICT211 Week 9 Lecture Notes.
• AXIS installation and user guides.
• Web Services and the Semantic Web
• http://www.w3.org/2002/ws/
• http://www.w3.org/2001/sw/
• Microsoft’s .NET
• http://msdn.microsoft.com/net/default.asp
• Java
• http://java.sun.com
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